1. Field of the Invention
The present invention relates in general to a radial lip seal and wear sleeve assembly and particularly to such an assembly which prevents undesired contact between a pair of seal lips and a coacting wear sleeve during shipping, installation and use.
2. Description of Prior Developments
A unitized radial lip seal and wear sleeve assembly is shown in U.S. Pat. No. 4,936,591 to Romero. This assembly includes an outer case installable in a housing and an inner case installable on a shaft extending through or within the housing. The inner case includes a tubular wall which is press-fit on the shaft to provide a sealing surface for a resilient elastomeric sealing element carried by the outer case. The tubular wall is sometimes referred to as a wear sleeve.
Use of a wear sleeve is advantageous in that it can be formed with a smooth surface free of pits, grooves or machine marks that might damage the seal lips or interfere with a desired sealing action between the seal lips and the shaft. The wear sleeve prevents direct contact between the seal lip and shaft so that the shaft does not have to be formed with a precision surface. The components in a unitized seal assembly are packaged together so that the mated seal surfaces are located within the assembly so as to be protected against damage and contamination during the installation process.
Axial forces are imposed on and between the inner and outer unitized seal cases as they are press-fit over a shaft and into a housing during seal installation. In many applications, the inner case and the outer case are further impacted together during shipping and handling. This may result in damage to the seal lips as they are axially abutted against the seal cases or wear sleeves.
Installation forces also cause the inner and outer cases to be axially compacted together so that, during initial operation of the seal assembly, the relative rotary motions of the inner and outer cases cause the axially abutted cases to rub and abrade. Such rubbing can generate loose particles that can adversely affect future performance of the seal assembly and can increase the torque required to rotate the shaft about which the seal assembly is installed.
A particular problem arises in the case of unitized seals which include seal lip elements formed from annular wafers of fluorinated resin polymers such as polytetrafluoroethylene (PTFE). These seal elements are particularly prone to damage from excessive contact forces applied by the seal case and/or wear sleeve during shipping, handling and/or installation. Such contact between the PTFE seal element and the metal case or wear sleeve can easily nick or damage the delicate tip of the seal element and thereby cause seal leakage and failure.